This invention relates to a storage system which stores data of a computer, and more particularly, to a storage subsystem composed of multiple disk devices and control of power supply to the multiple disk devices.
Conventional storage systems are equipped with a relatively high-performance and highly-reliable disk device (hard disk drive: HDD) that has a fibre channel (FC) interface (FC-HDD), as opposed to an inexpensive HDD that is mounted to personal computers (PC) and has an Advanced Technology Attachment (ATA) interface.
Recently, an inexpensive HDD that has a serial advanced technology attachment (SATA) interface (SATA-HDD), which is a high-speed version of the ATA interface, is beginning to gain popularity as an HDD for PCs. The SATA-HDD, when mounted to a storage system as a recording medium in place of the FC-HDD, provides an inexpensive, large-capacity storage system. This trend is especially prominent in mid-range to low-end storage systems where required performance is not particularly high and a lower-priced device is appreciated more.
On the other hand, storage systems for enterprises where high performance and high reliability are required use the high-performance, reliable FC-HDD, although enterprises now have an option of employing recently commercialized storage systems for enterprises which have the partial inexpensive SATA-HDD in addition to the FC-HDD and use the SATA-HDD for archive data storage where the required performance is not so high.
Power saving in IT systems has lately become an issue especially in data centers. Power saving leads to a cut in overall running cost of a system and ultimately to a reduced total cost of ownership (TOC) of the system. There has been a report that the data centers spend about 20% to 30% of electric power on their storage systems, so power saving in the storage systems is counted as one of future important issues.
A measure to solve this issue is disclosed in “Power-efficient Server-class Performance from Arrays of Laptop Disks”, University of Rochester, Technical Report 837, May 2004. The article discloses a technique of using in a storage system a mobile SATA-HDD, which consumes merely half to one-ninth of electric power consumed by the FC-HDD, instead of the high-performance and reliable but power-consuming FC-HDD.
The technique according to the article equipped with three mobile SATA-HDDs in place of one FC-HDD. Only one of the SATA-HDDs is in operation while required data read performance is low, and as higher read performance is demanded, the number of operating SATA-HDDs is increased from one to two or three. Here, one FC-HDD is substituted with three SATA-HDDs because the collective read performance of the three SATA-HDDs is higher than the read performance of one FC-HDD whereas collective power consumption of the three SATA-HDDs is less than the power consumption of one FC-HDD.